Differential Diagnosis of Keratoconus Based on New Technologies

Abstract

Keratoconus (KC) must be distinguished from other corneal ectatic diseases and thinning disorders for stage-appropriate and suitable management of each condition. The most relevant corneal pathologies that may imitate the tomographic KC pattern are pellucid marginal degeneration (PMD), keratoglobus, posterior keratoconus, and Fuchs-Terrien marginal degeneration (FTMD). In moderate cases of KC, differentiation is typically possible using slit lamp examination and corneal tomography with evaluation of the location of the corneal thinning region. In early cases, however, differential diagnosis may be more challenging since the cornea may look relatively normal. In severe cases, the extended area of corneal thinning also complicates differentiation. Biomicroscopic findings cannot always give all the information needed to distinguish KC from related ectatic corneal conditions. The aim of this work is to discuss contemporary techniques and findings to assist physicians to identify the correct diagnosis. Corneal topography has been used in recent decades as the main tool for imaging in ectatic corneal diseases. Moreover, Scheimpflug cameras (corneal tomographers), which analyze both anterior and posterior corneal surfaces, curvatures, pachymetry, elevation data, higher order aberrations, Fourier analysis of keratometric data, and corneal density have become the most promising tools for diagnosis and follow-up of ectatic diseases. A noninvasive air pulse tonometer in conjunction with an ultrahigh-speed Scheimpflug camera complements tomographic findings by analyzing biomechanical corneal properties. Α confocal microscopy system, which is a novel clinical technique for the study of corneal cellular structure, could contribute effectively in the same direction. Moreover, anterior segment optical coherence tomography (AS-OCT) creates cross-sections, which can be generated into a three-dimensional structure to produce corneal epithelial thickness (ET) measurements. ET mapping is increasingly recognized as a sensitive tool for the diagnosis of ocular surface disorders. Combining information of all these systems could lead to a more effective identification and differential diagnosis of ectatic corneal disorders.

Zusammenfassung

Die Unterscheidung zwischen Keratokonus (KK) und anderen ektatischen Hornhauterkrankungen ist für eine angemessene Behandlung der jeweiligen Erkrankung unerlässlich. Die wichtigsten Hornhautpathologien, die bei der Differenzialdiagnose des KK in Betracht gezogen werden müssen, sind die pelluzide marginale Degeneration (PMD), der Keratoglobus, der posteriore Keratokonus und die Fuchs-Terrienʼsche marginale Degeneration (FTMD). In mittelschweren KK-Fällen ist die Differenzierung aufgrund der klassischen Lage der Hornhautverdünnungsregion möglich. In frühen Fällen ist die Differenzialdiagnose jedoch schwierig, da die Hornhaut relativ normal aussehen kann. In fortgeschrittenen Stadien hingegen ist die Differenzierung aufgrund des ausgedehnten Bereichs der Hornhautverdünnung mitunter ebenfalls schwierig. Biomikroskopische Befunde können nicht alle Informationen liefern, die zur Unterscheidung des KK von anderen ektatischen Hornhauterkrankungen erforderlich sind. Daher werden moderne Techniken und Befunde diskutiert, um die richtige Differenzialdiagnose sicherstellen zu können. Hornhauttopografiekarten wurden in den letzten Jahrzehnten als Hauptinstrument für die bildgebende Differenzialdiagnose verwendet. Darüber hinaus wurden Scheimpflug-Kameras (Hornhauttomografen), die sowohl die vordere als auch die hintere Hornhautfläche anhand von Krümmungsdaten, Pachymetrie, Elevationsmessungen, Aberrationen höherer Ordnung, Fourier-Analysen keratometrischer Daten und die Hornhautdichte analysieren, zum wichtigsten Instrument für die Diagnose und Verlaufskontrolle ektatischer Hornhauterkrankungen. Seit neuestem zeichnet ein nicht invasives Luftstoßtonometer in Verbindung mit einer Ultrahochgeschwindigkeits-Scheimpflug-Kamera die Reaktion der Hornhaut auf diesen mechanischen Stimulus auf und analysiert so ihre biomechanischen Eigenschaften. Des Weiteren könnte die konfokale Mikroskopie effektiv zur Differenzialdiagnose beitragen. Darüber hinaus erzeugt die optische Kohärenztomografie des vorderen Segments (AS-OCT) Querschnitte, die in eine 3-dimensionale Struktur umgewandelt werden können, um die Hornhautepitheldicke zu messen. Das Endothel-Mapping wird zunehmend als wirksames Instrument für die Diagnose von Erkrankungen der Augenoberfläche anerkannt. Die Kombination der Informationen all dieser Systeme könnte eine umfassendere Identifizierung und Differenzialdiagnose ektatischer Hornhauterkrankungen ermöglichen.

Key words

keratoconus - pellucid marginal degeneration - keratoglobus - posterior keratoconus - Fuchs Terrien marginal degeneration - differential diagnosis

Schlüsselwörter

Keratokonus - pelluzide marginale Degeneration - Keratoglobus - posteriorer Keratokonus - Fuchs-Terrienʼsche marginale Hornhautdegeneration - Differenzialdiagnose

Publication History

Received: 22 December 2021

Accepted: 30 July 2022

Accepted Manuscript online:
08 August 2022

Article published online:
27 November 2022

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